In mobile communication systems in recent years, a separated-type base station apparatus has popularly been used in which the base station apparatus is structured with two devices, namely, a BaseBand Unit (BBU) and a Remote Radio Head (RRH). In this situation, the BBU is a device that connects to a superordinate core network and performs a baseband processing process. The RRH is a device that makes wireless connection to a mobile terminal and amplifies an analog radio signal. Further, as another example of a BBU, a Centralized BaseBand Unit (C-BBU) that is installed so as to centralize in a remote location different from the installment location of an RRH is also popularly used.
Further, in order to enlarge the coverage area of a mobile communication system, a repeater may be used in some situations, besides the base station apparatus. The repeater enlarges the coverage area of the base station by receiving a radio signal from a master base station, amplifying the received radio signal, and transmitting the amplified radio signal. It is determined whether a base station shall be used or a repeater shall be used, depending on the traffic amount and/or the number of users in the coverage area.
When the coverage area of a mobile communication system is enlarged in this manner, a selection is made between using a base station that employs an RRH or the like and using a repeater. When a repeater is used, because no baseband processing device needs to be used, it is possible to omit the communication lines connecting to BBUs and a core network. For this reason, installing a repeater is simpler than installing a base station.
However, because the repeater simply amplifies and transmits the radio signal, the capacity of the mobile communication system itself does not increase. For this reason, when the traffic increases in an area subordinate to the repeater, there is a possibility that the problem of a shortage of capacity may arise, in areas including the coverage area of the master base station.
To cope with this situation, to enlarge the coverage area of a region where traffic of a certain level or larger is, even temporarily, expected, it is desirable to secure the capacity by installing a base station apparatus instead of a repeater.
As additional information, for example, a conventional technique related to a mobile communication system that employs a repeater is known, by which sub-carriers used by a base station apparatus are limited when a repeater is present, so that the repeater performs communication by using sub-carriers that are not used by the base station apparatus. With this arrangement, it is possible to effectively utilize the frequency resources. Further, another conventional technique is also known by which, when a large load is detected at a transmission origin of wireless signals, the output power for re-transmissions by a repeater is lowered.    Patent Document 1: Japanese Laid-open Patent Publication No. 2008-177969    Patent Document 2: International Publication No. WO/2005/034554
However, when base station apparatuses are installed, the base station apparatuses including RRHs are always in operation to secure the coverage area accommodated thereby, even if there is no user subordinate thereto. Thus, the resources used by BBUs and an increase in the electric power consumption may become problems.